Larger infarct size but equal protection by ischemic conditioning in septum and anterior free wall of pigs with LAD occlusion.

The ischemic area at risk (AAR) is one major determinant of infarct size (IS). In patients, the largest AAR is seen with a proximal occlusion of the left anterior descending (LAD) coronary artery, which serves parts of the septum and of the anterior free wall. It is not clear, whether regional differences in the perfusion territories also impact on IS and the magnitude of cardioprotection by ischemic conditioning. We have retrospectively analyzed 132 experiments in pigs, which have a similar LAD perfusion territory as humans. The LAD was occluded for 60 min with subsequent 180 min reperfusion. Cardioprotection by either local ischemic pre- or postconditioning or remote ischemic pre- or perconditioning was induced in 93 pigs. The AAR was demarcated by blue dye staining, and IS was assessed by triphenyltetrazolium chloride (TTC) staining. Using digital planimetry, the AAR was separated into sections unequivocally located in the septum (AARS ) or the anterior free wall (AARAFW ). Relative IS was calculated for AARS or AARAFW . AARAFW was larger than AARS (51 ± 9% vs. 34 ± 8% of total AAR; mean ± SD, P < 0.001). Regional myocardial blood flow (microspheres) was not different between septum and anterior free wall. IS without ischemic conditioning tended to be larger in AARS than in AARAFW (50 ± 17% vs. 44 ± 19%; % of AARAWF or AARS , respectively; P = 0.075). Also, with robust IS reduction by ischemic conditioning, the difference in relative IS remained (AARS : 27 ± 16%; AARAFW : 21 ± 16%; P = 0.01). There is a somewhat greater susceptibility for infarction in septal than anterior free wall myocardium. However, ischemic conditioning still reduces IS in both septal and anterior free wall myocardium.

Vago-Splenic Axis in Signal Transduction of Remote Ischemic Preconditioning in Pigs and Rats.

RATIONALE: The signal transduction of remote ischemic conditioning is still largely unknown. OBJECTIVE: Characterization of neurohumoral signal transfer and vago-splenic axis in remote ischemic preconditioning (RIPC). METHODS AND RESULTS: Anesthetized pigs were subjected to 60 minutes of coronary occlusion and 180 minutes of reperfusion (placebo+ischemia/reperfusion [PLA+I/R]). RIPC was induced by 4×5/5 minutes of hindlimb I/R 90 minutes before coronary occlusion (RIPC+I/R). Arterial blood samples were taken after placebo or RIPC before I/R. In subgroups of pigs, bilateral cervical vagotomy, splenectomy, or splenic denervation were performed before PLA+I/R or RIPC+I/R, respectively. In pigs with RIPC+I/R, infarct size (percentage of area at risk) was less than in those with PLA+I/R (23±12% versus 45±8%); splenectomy or splenic denervation abrogated (splenectomy+RIPC+I/R: 38±15%; splenic denervation+RIPC+I/R: 43±5%), and vagotomy attenuated (vagotomy+RIPC+I/R: 36±11%) RIPC protection. RIPC increased phosphorylation of STAT3 (signal transducer and activator of transcription 3) in left ventricular biopsies taken at early reperfusion. Splenectomy or splenic denervation, but not vagotomy, abolished this increased phosphorylation. In rats with vagotomy, splenectomy, or splenic denervation, RIPC (3×5/5 minutes of hindlimb occlusion/reperfusion) or placebo was performed, respectively. Hearts were isolated, saline perfused, and subjected to 30/120-minute global I/R. With RIPC, infarct size (percentage of ventricular mass) was less (20±7%) than with placebo (37±6%), and vagotomy, splenectomy, or splenic denervation abrogated RIPC protection (38±12%, 36±9%, and 36±7%), respectively. Rat spleens were isolated, saline perfused, and splenic effluate (SEff) was sampled after infusion with carbachol (SEffcarbachol) or saline (SEffsaline). Pig plasma or SEff was infused into isolated perfused rat hearts subjected to global I/R. Infarct size was less with infusion of RIPC+I/Rplasma+ (24±6%) than with PLA+I/Rplasma (40±8%), vagotomy+PLA+I/Rplasma (39±11%), splenectomy+PLA+I/Rplasma (35±8%), vagotomy+RIPC+I/Rplasma (40±9%), splenectomy+RIPC+I/Rplasma (33±9%), or splenic denervation+RIPC+I/Rplasma (39±8%), respectively. With infusion of SEffcarbachol, infarct size was less than with infusion of SEffsaline (24 [19-27]% versus 35 [32-38]%). CONCLUSIONS: Activation of a vago-splenic axis is causally involved in RIPC cardioprotection.